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The magnetization, Hall effect, and resistivity of Heusler alloys Co2FeZ (where Z = Al, Si, Ga, Ge, In, Sn, and Sb are s- and p-elements) have been studied at T= 4.2 K in magnetic fields H≤ 100 kOe. In strong fields (H> 20 kOe), magnetization can be described by the Stoner model. The normal R0and anomalous RSHall effect coefficients have been determined. The coefficient RS is positive for almost all the studied alloys and represents a “linearly quadratic” resistivity function incorporating linear and quadratic terms. The constant R0is negative for most alloys, and its absolute value is two or three orders of magnitude smaller than for RS. The magnetoresistivity of the studied alloys does not exceed several percent and may be both positive and negative for different specimens.

NMR studies of 125Te in the topological insulator bismuth telluride Bi2Te3in a wide temperature range from room temperature to 12.5 K are performed. The pulsed NMR spectrometer Bruker Avance 400 is applied. The NMR spectra are obtained for the powder from Bi2Te3 single crystal and monocrystalline plates with the orientations c|| Band c⊥ B. At room temperature, the spectra consist of two lines related to two nonequivalent positions of tellurium nuclei Te1 and Te2. The parameters of the NMR frequency shift tensor are found from the powder spectrum. The temperature dependences of the spectra for the powder and plates with the orientation c ⊥ B agree with each other. The line shift with decreasing temperature is explained by the reduction of the Knight shift. The thermal activation energy of charge carriers is estimated. The spectra for the plates with the orientation c || B demonstrate peculiar behavior below 91 K. The spin-lattice relaxation time for the powder and monocrystalline plates with both orientations at room temperature is measured.

The electrical resistivity ρ(T) of the band ferromagnets Co2FeZ (where Z= Al, Si, Ga, Ge, In, Sn, and Sb are s- and p-elements of Mendeleev’s Periodic Table) has been investigated in the temperature range 4.2 K < T < 1100 K. It has been shown that the dependences ρ(T) of these alloys in a magnetically ordered state at temperatures T< TCare predominantly determined by the specific features of the electronic spectrum in the vicinity of the Fermi level. The processes of charge carrier scattering affect the behavior of the electrical resistivity ρ(T) only in the vicinity of the Curie temperature TCand above, as well as in the low-temperature range (at T≪ TC).

A powder sample and single-crystal plates of the topological insulator Bi2Te3have been investigated using the 125Te NMR method at room temperature and at low temperatures in the range from 12.5 to 16.5 K. The NMR spectra of the single-crystal plates have been studied in the orientation where the crystallographic axis c is directed parallel or perpendicular to the magnetic field. The spectra have been obtained by means of recording spin-echo signals and plotting their envelopes. It has been shown that the NMR spectra for the bismuth telluride powder and plates with the orientation c⊥ Bconsist of two lines, which are presumably attributed to tellurium nuclei in two crystallographic positions in the bulk of the sample. The position and shape of the lines are determined by the chemical shift and the Knight shift. For the orientation of the plates c|| B, the spectrum contains an additional component in the high-frequency region, which cannot appear due to the angular dependence of the line shifts caused by tellurium nuclei in the bulk of the topological insulator. At a low temperature, the additional line dominates in the spectrum.

The Hall effect and the magnetoresistance of ferromagnetic Heusler alloys Co2YAl, where Y= Ti, V, Cr, Mn, Fe, and Ni have been studied at T= 4.2 K in magnetic fields H≤ 100 kOe. Normal R0and anomalous RSHall coefficients are shown to be maximal in magnitudes in the middle of the 3dperiod of the periodic table of elements. Coefficient R0changes the negative sign to positive sign in going from weak (Y= Ti, V) to strong (Y= Cr, Mn, Fe, and Ni) ferromagnetic alloys. Constant RSis positive and proportional to ρ2.9in all the alloys. The magnetoresistance of the alloys is not higher than several percent and its magnitude is changed fairly significantly in the dependence on the number of valence electrons z; the magnetoresistance signs vary arbitrarily.

The temperature dependences of the magnetization of ferromagnetic Heusler alloys Co2YAl, where Y= Ti, V, Cr, Mn, Fe, and Ni have been studied at H= 50 kOe in the range 2 K < T< 1100 K. It is shown that the high-field (H≥ 20 kOe) magnetization is described within the Stoner model.

The transport properties of half-metallic ferromagnetic Heusler alloys Co2MeAl (Me= Ti, V, Cr, Mn, Fe are transition 3dmetals) have been measured in the temperature range of 4–900 K. The specific features of the behavior of the resistivity have been considered in the framework of the two-current model of conductivity that takes into account the existence of the energy gap in the electronic spectra of the alloys near the Fermi level of one of electron subbands that differs in the spin direction.